The invention generally relates to annotating a recording, such as a photograph, video, etc. with data indicating a location where recording occurred, and more particularly to tracking multiple different signal sources to facilitate determining the location when a primary locating technique fails.
When taking a recording of a place or an event, it is often desirable to associate a location, typically the location at which the recording is made, with the recording so that one may later review the recording and be reminded of where it occurred. Associating locations with recordings is often a tedious prospect, especially when several different places are visited and the recordings are not available for annotation until later-on, such as returning from a trip. Often, due to tediousness, or poor memory after the fact, associations are not performed at all.
There has been an attempt to facilitate making such associations with digital camera photographs. Here, GPS (Global Positioning System) track log data is used to cross-reference a time at which a digital camera indicates a photograph occurred photograph with timed entries in the GPS track log, thus identifying where the photograph occurred. There are significant limitations to this approach, some of which are inherent to GPS systems.
For example, GPS systems take a long time to start up, thus initial pictures may occur with no GPS data available to indicate where the picture occurred. Also, GPS systems require adequate reception from at least four satellites in order to accurately determine spatial position in three dimensions. Obtaining adequate signal from four satellites is often difficult depending on the terrain through which one travels, as various conditions, such as physical obstructions, thick tree cover, tall buildings, etc., may cause a satellite to become obscured and thus preclude obtaining GPS position data. Related to this is that when a GPS receiver loses track of its satellites, the receiver may then either give out invalid position information, e.g., zero-values, or repeat last known valid position data, which may be quite wrong if one is traveling quickly. Such GPS data can result in wildly incorrect position data being associated with pictures.